DBCS - Wikipedia

    A double-byte character set  (DBCS)
    is a character encoding in which
    either all characters (including control characters)
    are encoded in two bytes,
    or merely every graphic character not representable by
    an accompanying single-byte character set (SBCS)
    is encoded in two bytes (Han characters would generally comprise most of these two-byte characters).
    A DBCS supports national languages that contain many unique characters or
    symbols (the maximum number of characters that can be represented with one byte is 256 characters,
    while two bytes can represent up to 65,536 characters).
    Examples of such languages include Japanese and
    Chinese.
    Korean Hangul does not contain as many characters,
    but KS X 1001 supports both Hangul and
    Hanja,
    and uses two bytes per character.


In CJK (Chinese/Japanese/Korean) computing

    The term DBCS traditionally refers to a character encoding where each graphic character
    is encoded in two bytes.

    In an 8-bit code,
        such as Big-5 or
        Shift JIS,
    a character from the DBCS is represented with
        a lead (first)  byte with the most significant bit set
        (i.e.,  being greater than  seven bits),
        and paired up with
            a single-byte character-set (SBCS).
    For the practical reason of maintaining compatibility with
        unmodified,
        off-the-shelf software,
            the SBCS
                is associated with  half-width characters and
            the DBCS
                with full-width characters.

    In a 7-bit code such as ISO-2022-JP,
        escape sequences or
        shift codes
            are  used to  switch between
                the SBCS and
                DBCS. 

    Sometimes,
    the use of the term "DBCS" can imply an underlying structure that
        does not comply with ISO 2022.
    For example,
        "DBCS" can sometimes mean
            a double-byte encoding that
                is  ¿specifically not¿ Extended Unix Code (EUC).


    This original meaning of DBCS is different from
        what some consider correct usage today.

    Some insist that
        these character encodings be properly called
            ¿multi-byte character sets (MBCS)¿
         or ¿variable-width encodings¿
    because
        character encodings such as EUC-JP,
                                    EUC-KR ,
                                    EUC-TW,
                                    GB 18030,
                                and UTF-8 
            use more than  two bytes for some characters,
            and they support one byte for other characters.


Ambiguity 

    Some people use DBCS to mean the UTF-16 and  UTF-8 encodings,
    while other people use the term DBCS to
        mean older (pre-Unicode)  character encodings that use more than  one byte per character.
            Shift JIS,
            GB 2312 and
            Big5 
                are a few character encodings that can contain more than  one byte per character,
        but even using the term DBCS for these character encodings is incorrect terminology
        because  these character encodings are really variable-width encodings
        (as are both UTF-16 and  UTF-8).
    Some IBM mainframes do have true DBCS code pages,
    which contain only the double byte portion of a multi-byte code page.


    If a person uses the term "DBCS enablement" for software internationalization,
    they are using ambiguous terminology.
    They either mean they want to write software for East Asian markets using older technology with code pages,
    or they are planning on using ¿Unicode¿
    Sometimes this term also implies translation into an East Asian language.
    "Unicode enablement" means
                internationalizing software by  using Unicode,
    "DBCS enablement" means
               using ¿incompatible¿ character encodings that exist between
                the various countries in East Asia for internationalizing software.
    Since Unicode,
    unlike many other character encodings,
        supports all the major languages in East Asia,
            it is generally easier to enable and
            maintain software that uses Unicode.
    DBCS (non-Unicode)  enablement is usually only desired when
        much older operating systems or
        applications do not support Unicode. 

TBCS 
    A triple-byte character set
    (TBCS)
    is a character encoding in which
    characters (including control characters)
    are encoded in three bytes. 

See also

    * Variable-width encoding
    * DOS/V

External links

    * Microsoft's definition of "double-byte character set"
    * IBM's definition of "double-byte character set" at the Wayback Machine (archived October 18, 2018) 



 
